In recent years, improvements in a communication data rate and an increase in a transmission distance with the growing scale of a system have been remarkable in an information processing system where a plurality of information processing devices (computers) are connected by a communication network. In association with this, an optical communication has been widely used as a replacement for an electric communication in a middle-to-long range communication between information processing devices. In a large-scale system, also a point that a weight of an optical cable can be made lighter than that of an electric cable is an advantage in the use of an optical communication.
FIG. 1 illustrates a configuration example of an information processing system using a conventional optical communication. The information processing system illustrated in FIG. 1 includes an information processing device 101, an information processing device 102, and an optical transmission link 103.
The information processing device 101 includes a transmission and reception circuit 111 and an interface circuit 112, whereas the information processing device 102 includes a transmission and reception circuit 121 and an interface circuit 122. The optical transmission link 103 is a communication line between the information processing device 101 and the information processing device 102, and includes four signal paths. Each of the signal paths included in the optical transmission link 103 is sometimes referred to as a lane.
The transmission and reception circuit 111 and the interface circuit 112 are connected by wires 113-1 to 113-4, whereas the transmission and reception circuit 121 and the interface circuit 122 are connected by wires 123-1 to 123-4. A wire 113-i and a wire 123-i (i=1 to 4) belong to an ith lane among the four lanes included in the optical transmission link 103.
The interface circuit 112 and the interface circuit 122 respectively include a transmission conversion element for converting an electric signal to be transmitted to the optical transmission link 103 into an optical signal, and a reception conversion element for converting an optical signal received from the optical transmission link 103 into an electric signal. One transmission conversion element and one reception conversion element are provided for every specified number of lanes in many cases. In this example, one conversion element 201 is provided for the four lanes as illustrated in FIG. 2.
However, the conversion elements provided in the interface circuit 112 and the interface circuit 122 have a characteristic such that failures are relatively prone to occur. By way of example, for a 10-Gbps conversion element, a failure rate per lane is approximately 50 fit. In a small-scale system using approximately 20 conversion elements, a failure rate of the conversion elements does not matter. However, in a large-scale system using several thousands to several tens of thousands of conversion elements, a failure rate of the conversion elements matters.
One of forms of failures of the conversion element 201 is a 1-lane failure by which only one lane among a plurality of lanes connected to the conversion element 201 enters a state (disconnected state) disabled to transmit and receive a signal. As measures taken against the 1-lane failure, a technique of dynamic lane degeneration, which is adopted by interface standards such as Peripheral Components Interconnect Express (PCI-Express), InfiniBand, and the like, is widely used. By performing the dynamic lane degeneration, a communication can be continued with remaining normal lanes when some of a plurality of lanes used as an optical transmission link are disconnected.
In the meantime, as illustrated in FIG. 4, also an all-lane failure by which all lanes of the conversion element 201 enter into a disconnected state due to a failure of a power system or a control system of an information processing device sometimes occurs. Accordingly, in an information processing system adopting conversion elements, measures to suppress an influence of a failure is sometimes taken by making optical transmission links redundant based on the assumption that the failure of a conversion element occurs.
FIG. 5 illustrates a configuration example of the information processing system where optical transmission links are made redundant. The information processing system illustrated in FIG. 5 includes the information processing device 101, the information processing device 102, the optical transmission link 103, and an optical transmission link 501.
The information processing device 101 illustrated in FIG. 5 has a configuration implemented by adding an interface circuit 511 to the information processing device 101 illustrated in FIG. 1, whereas the information processing device 102 illustrated in FIG. 5 has a configuration implemented by adding an interface circuit 521 to the information processing device 102 illustrated in FIG. 1.
The transmission and reception circuit 111 and the interface circuit 511 are connected by wires 512-1 to 512-4, whereas the transmission and reception circuit 121 and the interface circuit 521 are connected by wires 522-1 to 522-4. An ith (i=1 to 4) lane among four lanes included in the optical transmission link 501 runs through a wire 512-i and a wire 522-i. 
With such an information processing system, a communication can be made by using eight lanes including the four lanes of the optical transmission link 103 and those of the optical transmission link 501 between the information processing device 101 and the information processing device 102. In this case, even if an all-lane failure of a conversion element of the interface circuit 112 or the interface circuit 511 of the information processing device 101 occurs, a communication can be continued by using the four lanes connected to the other interface circuit.
A wireless relay system that can continue a mobile communication service within a closed space even if a failure of a transmission line or an antenna for a mobile station occurs in a mobile communication system is known (for example, see Patent Document 1). In this wireless relay system, a plurality of antennas are provided within a closed space such as an underground city, a tunnel, or the like that radiowaves from a base station do not reach. These antennas are partitioned into a plurality of groups, and arranged so that a service area of each of the antennas overlaps that of an antenna that belongs to a different group and is adjacent. Then, the wireless relay device feeds power to antennas that belong to each of the groups through a transmission line corresponding to each of the groups.
Also a ring network having a capability of recovering a failure of a multiplexing device that drops, adds, or regenerates and relays an optical signal is known (for example, see Patent Document 2). A node device in this ring network includes an optical switch for switching an optical transmission line to and from which an optical signal is input and output, a wavelength demultiplexer for demultiplexing a wavelength-multiplexed signal output from an optical switch, and a wavelength multiplexer for wavelength-multiplexing an optical signal input to an optical switch. The node device further includes a multiplexing device, which is provided between the wavelength demultiplexer and the wavelength multiplexer, for dropping, adding, or regenerating and relaying an optical signal having a demultiplexed wavelength.
A transmission system for maintaining a connection of the entire link by bypassing a failure that has occurred in some of lanes, by using only a normal lane, and by reducing a communication capacity in a multi-lane transmission is also known (for example, see Patent Document 3). In this transmission system, a transmitter and a relay device are connected by a first transmission line, the relay device and a receiver are connected by a second transmission line, and the transmitter, the relay device, and the receiver have virtual lanes. The transmitter partitions transmission data into data strings, the number of which is that of available virtual lanes, based on information of used lanes. The relay device monitors a failure of each transmission lane of the first transmission line and each virtual lane. The receiver monitors a failure of each transmission lane of the second transmission line and each virtual lane, decides an available virtual lane, transmits information of used lanes to the transmitter, and restores the partitioned data strings to the transmission data.
Patent Document 1: Japanese Laid-open Patent Publication No. 7-240710
Patent Document 2: Japanese Laid-open Patent Publication No. 11-225118
Patent Document 3: Japanese Laid-open Patent Publication No. 2010-232787